Costaceae (K. Schum.) Nak.
Habit and leaf form. Herbs; without essential oils. Plants succulent to non-succulent. Perennial; rhizomatous. Self supporting, or epiphytic. Mesophytic. Leaves alternate; spiral, or four-ranked; ‘herbaceous’, or fleshy; petiolate, or sessile; sheathing. Leaf sheaths with joined margins. Leaves without marked odour; simple; epulvinate. Lamina entire; lanceolate to ovate; pinnately veined (‘pinnate-parallel’); without cross-venules. Leaves conspicuously ligulate. Lamina margins entire. Vernation convolute.
General anatomy. Plants with silica bodies (internal, stellate or druselike).
Leaf anatomy. Epidermis without differentiation into ‘long’ and ‘short’ cells; without silica bodies. Stomata present; paracytic, or tetracytic. Guard-cells not ‘grass type’.
The mesophyll without etherial oil cells; not containing mucilage cells; containing calcium oxalate crystals. The mesophyll crystals druses, or solitary-prismatic (? — no raphides). Midrib conspicuous, or not conspicuous. Minor leaf veins without phloem transfer cells (Costus, Tarpeinocheilos). Vessels absent.
Stem anatomy. Cork cambium absent. Secondary thickening absent. Xylem with vessels, or without vessels. Vessel end-walls scalariform.
Root anatomy. Root xylem with vessels; vessel end-walls scalariform.
Reproductive type, pollination. Fertile flowers hermaphrodite. Plants hermaphrodite. Floral nectaries present. Nectar secretion from the gynoecium (from septal nectaries, often two well developed and one reduced). Pollination entomophilous, or cheiropterophilous.
Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’. The ultimate inflorescence unit cymose. Inflorescences terminal, or axillary. Flowers bracteate (the bracts with a linear extrafloral nectary beneath the tip); bracteolate, or ebracteolate; very irregular; zygomorphic. The floral irregularity involving the perianth and involving the androecium. Flowers basically 3 merous (but much modified); cyclic. Perigone tube absent.
Perianth with distinct calyx and corolla; 6; free; 2 whorled; isomerous; different in the two whorls. Calyx 3; 1 whorled; gamosepalous; blunt-lobed; unequal but not bilabiate (spathelike, or constituting a tube split to the base on one side); imbricate; with the median member anterior. Corolla 3; 1 whorled; gamopetalous; unequal but not bilabiate (the median lobe larger and often upcurved).
Androecium 1 (ostensibly), or 6 (theoretically, but scarcely recognisable as such). Androecial members free of the perianth; united with the gynoecium (in that the thin style is fused to a groove along the length of the single anther); markedly unequal; free of one another and coherent, or coherent (depending on interpretation); supposedly 2 whorled. Androecium including staminodes. Staminodes supposedly 5; petaloid. Stamens 1 (the median, posterior member of the theoretical inner whorl); reduced in number relative to the adjacent perianth; petaloid. Anthers adnate; non-versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate. Anther epidermis persistent. Microsporogenesis successive. Anther wall initially with more than one middle layer. Tapetum glandular. Pollen grains aperturate; 1 aperturate, or 5–16 aperturate; sulcate, or foraminate, or spiraperturate; 2-celled.
Gynoecium 3 carpelled. The pistil (1–)3 celled. Gynoecium syncarpous; eu-syncarpous; inferior. Ovary (1–)3 locular. Epigynous disk often present. Styles 1; apical. Stigmas 1; wet type; papillate; Group III type. Placentation when unilocular parietal; usually, when trilocular axile. Ovules 15–50 per locule (i.e. ‘many’); arillate; anatropous; bitegmic; crassinucellate. Outer integument not contributing to the micropyle. Embryo-sac development Adoxa-type. Polar nuclei fusing prior to fertilization. Antipodal cells not formed (the nuclei ephemeral). Synergids hooked. Hypostase present. Endosperm formation helobial. Embryogeny caryophyllad.
Fruit fleshy, or non-fleshy; dehiscent, or indehiscent; a capsule, or a nut, or capsular-indehiscent, or achene-like (?— ‘a capsule, or dry and indehiscent’). Seeds endospermic. Endosperm not oily (starchy). Perisperm present. Seeds with starch. Cotyledons 1. Embryo straight. Testa encrusted with phytomelan; black.
Seedling. Hypocotyl internode present (long). Seedling collar not conspicuous. Cotyledon hyperphyll compact (small); non-assimilatory (but borne atop the large, leaflike, assimilatory sheath). Coleoptile absent. First leaf dorsiventral. Primary root ephemeral.
Physiology, biochemistry. Cyanogenic (Costus). Saponins/sapogenins present (Costus).
Geography, cytology. Tropical. Widespread tropical. X = 8, 9.
Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Zingiberiflorae; Zingiberales. APG 3 core angiosperms; Superorder Lilianae; commelinid Monocot; Order Zingiberales.
Species 200. Genera 4; Costus, Dimerocostus, Monocostus, Tapeinocheilos.
• Costus afer: Bot. Reg. 683, 1822.
• Costus speciosus: Bot. Reg. 665, 1822.